In a loom, a warp beam around which warps are wound is rotated by a feed motor so that the warps are fed out, wefts are inserted into openings of the warps formed by heddles, and the wefts are beaten down by a reed whereby a woven fabric is formed. The formed woven fabric is pulled in and taken up by rotation of a roller which abuts against the woven fabric by a pull-in motor.
Tension of the warps is preferably controlled constant from the viewpoint of keeping the quality of woven fabric constant. The tension of the warp is controlled by controlling the feed motor and the pull-in motor based on a detection value of the tension of the warps. Patent Document 1 discloses technology filtering the detection value of the tension by a low pass filter so as to for eliminate the effects of the heddles or reed on the tension and stabilize control of the tension.    Patent Document 1: Japanese Patent Publication (A) No. 2001-288645